The present invention relates to a chuck for the clamping of tools by shrink fit.
A chuck of this type is described in U.S. Pat. No. 5,311,654. In these chucks, the chuck member has a longitudinal section with a central receptacle having a clamping surface for inserting and holding the tool to be clamped with its cylindrical shank. The receptacle is made of a central, axially relatively long-dimensioned bore hole which is in communication with a central channel in the remaining part of the chuck member, this bore hole being intended at the same time to be used for the passage of a lubricant and/or coolant, as well. For this purpose, introduced in the region of the central bore hole are four shallow longitudinal grooves, arranged at equal angular distances from each other in the circumferential direction, through which the lubricant and/or coolant is guided along the shank of the clamped tool to the front up to the freely projecting tool part. In this contraction chuck, to initiate the shrink clamping, the longitudinal section containing the central bore hole is heated from the outside, so that it expands radially under heating, with accompanying radial widening of the central bore hole which forms the clamping surface. Because of the relatively large material cross-section of the longitudinal section, it has only a relatively low expansion rate. The extent of the radial widening of the central bore hole is relatively small. This demands that the shanks of the tools to be clamped in this manner must be very exactly machined and dimensioned, in conformity with the widening capability of the central clamping bore hole of the chuck. The tolerances for the diameters of the tools are therefore very narrow. Depending on circumstances, the application time of the heat and/or the amount of heat when heating the longitudinal section of the chuck is relatively great for achieving the suitably sufficient widening. Following the heating and insertion of the tool, shrinkage of the longitudinal section of the chuck member results during subsequent cooling, with accompanying radial contraction and clamping of the cylindrical shank of the tool in the region of the central bore hole.
It is an object of the present invention to provide a chuck of the type indicated above which has an increased rate of expansion with accompanying larger widening of the clamping diameter, permitting greater tolerances for the shank of the tools to be clamped.
The above and other beneficial objects of the present invention are achieved by providing a chuck as described herein.
Due to the configuration of the chuck according to the present invention, in response to the heating, the longitudinal section containing the central receptacle expands to a greater extent with increased rate of expansion, and the effective diameter for the expansion is greater. A larger widening of the clamping diameter results. This arrangement may provide the advantage that the shank tolerance for the tools to be clamped may be greater. Depending on circumstances, the application time and/or quantity of heat necessary for heating the longitudinal section of the chuck may also be reduced. Above all, the chuck is inexpensive and uncomplicated.